1.Field of the Invention
The present invention generally relates to systems and methods for drilling and completing a wellbore. More particularly, the invention relates to systems and methods for mitigating trouble zones in a wellbore in a managed pressure condition and completing the wellbore in the managed pressure condition.
2.Description of the Related Art
Historically, wells have been drilled with a column of fluid in the wellbore designed to overcome any formation pressure encountered as the wellbore is formed. This “overbalanced condition” restricts the influx of formation fluids such as oil, gas or water into the wellbore. Typically, well control is maintained by using a drilling fluid with a predetermined density to keep the hydrostatic pressure of the drilling fluid higher than the formation pressure. As the wellbore is formed, drill cuttings and small particles or “fines” are created by the drilling operation. Formation damage may occur when the hydrostatic pressure forces the drilling fluid, drill cuttings and fines into the reservoir. Further, drilling fluid may flow into the formation at a rate where little or no fluid returns to the surface. This flow of fluid into the formation can cause the “fines” to line the walls of the wellbore. Eventually, the cuttings or other solids form a wellbore “skin” along the interface between the wellbore and the formation. The wellbore skin restricts the flow of the formation fluid during a production operation and thereby damages the well.
Another form of drilling is called managed pressure drilling. An advantage of managed pressure drilling is the ability to make bottom hole pressure adjustments with minimal interruptions to the drilling progress. Another related drilling method of managed pressure drilling is underbalanced drilling. In this drilling method, the column of fluid in the wellbore is designed to be less than the formation pressure encountered as the wellbore is formed. Typically, well control is maintained by using a drilling fluid with a predetermined density to keep the hydrostatic pressure of the drilling fluid lower than the formation pressure. As the wellbore is formed, drill cuttings and small particles or “fines” are created by the drilling operation and circulated out of the wellbore resulting in minimal formation damage.
Managed pressure drilling and underbalanced drilling maximizes the production of the well by reducing skin effect and/or formation damage during the drilling operation. However, the maximization of production is negated when the well has to be killed in order to mitigate a trouble zone encountered during the managed pressure or underbalanced drilling operation. Further, the maximization of production is negated when the well has to be killed in order to complete the wellbore after the drilling operation. Presently, snubbing is a method for tripping a drill string in a constant underbalanced state. Snubbing removes the possibility of damaging the formation, but increases rig up/rig down and tripping times, adding to the operational expense. In addition, the snubbing unit cannot seal around complex assemblies, such as a solid expandable drilling liner which is typically used to mitigate a trouble zone encountered during a drilling operation. Further snubbing units cannot seal around slotted liners or conventional sand screens which are typically used in completing a wellbore.
There is a need, therefore, for an effective method and system to mitigate trouble zones encountered during an underbalanced or managed pressure drilling operation. There is a further need, therefore, for an effective method and system to complete the wellbore in an underbalanced or managed pressure condition.